The present invention relates to screening equipment such is used in connection with water treatment plants and wastewater treatment facilities. The general purpose of such screening equipment is to remove solids from the fluid stream so that the solids may be processed separately from the fluid stream.
A typical water or waste water treatment plant includes some means to screen solids from the fluid flowing into a treatment facility; this is often the first stage of treatment. For example, it is often important to catch and remove rocks, paper, cotton, cloth, or other debris from a fluid stream to protect downstream processing equipment. For another example, solids may be separated from a diversion water stream (CSO screening), wherein the solids are returned to the stream for subsequent treatment, allowing the excess liquid of a storm to by-pass sewage treatment works or to flow to storage for subsequent treatment.
Certain types of solids cause particular problems for fluid screening equipment. In particular, the widespread use of non-soluble, not readily biodegradable plastic tampon applicators is now causing significant visual and physical problems in conventional sewage treatment plants. The screening mechanisms widely used in the later half of the twentieth century were not intended for removing xc2xdxe2x80x3 inch diameter and smaller solids, and consequently these solids are now reporting in filters, digesters, and even in plant discharges to receiving streams, lakes, and oceans. Depending on the type of equipment used, this causes obvious problems for the operation of the screening equipment, environmental problems, or both.
Rocks and gravel sometimes cause extreme difficulties for bar screens and screenings compactors. There is a present need for a device to remove these materials prior to screening.
A number of machines have been developed in recent years for the general purpose of removing solids from a fluid stream. Representative machines are disclosed in U.S. Pat. Nos. 4,188,294; 3,856,678; and 3,615,022 of Hagihara (plastic element filter screens); U.S. Pat. No. 1,207,376 of Davidson; U.S. Pat. No. 4,812,231 of Wiesemann (metal element screen); Link Belt traveling water screens of about 1956 or 57; and U.S. Pat. No. 2,929,504 of Lind et al. (screw screens).
Each of the above designs has certain inherent weaknesses which causes the design to be sub-optimal. For example, the plastic filter element of Hagihara has a high mortality rate and is difficult and time consuming to replace; and the filter screens derived from Wiesemann are reportedly high maintenance. Both types of screens require either pivotable or removable mountings to remove the screenings that become trapped between the down-going and up-going sections of the filtering chain conveyer. For another example, traveling water screens have tray cleaning problems associated with the fine openings of the trays, and also have sealing problems at the moving joints. For yet another example, screw screen designs impose severe lay-out constraints. Finally, the rack of spaced parallel bars that are cleaned by a rake are problematic when used with very small openings because the relatively narrow cleaning teeth, which must be narrower then the bar spacings, are weak and readily damaged.
The above efforts in the development of screening devices, and the problems that have not been solved, show that a simple, reliable, and economical screening mechanism would be a welcome advance in the art.
The present invention is a device and method for clearing debris from fluid channels. In one embodiment, the device is a screening member that is permeable in part wherein debris will collect. A movable scraper then scrapes along the screen and removes the debris therefrom and transports the debris to a desired location. An embodiment of the invention, the surface that comprises the screen member, may be arcuate, and may be a surface of revolution. Different portions of the screening number may or may not be permeable. The invention may also include an overflow mechanism where overflow water is diverted into a separate unscreened fluid stream. Further, the invention may be suitable for use within a sump.